mash: Remove some WmWindow usage in ash/shelf.

ash/shelf/wm_shelf.cc

Index: ash/shelf/wm_shelf.cc
diff --git a/ash/shelf/wm_shelf.cc b/ash/shelf/wm_shelf.cc
index 6abaf16ab8075c8dd9c56c24ab28d08efcad4597..57719054ccb4191d657e400ecd254f244f916ff9 100644
--- a/ash/shelf/wm_shelf.cc
+++ b/ash/shelf/wm_shelf.cc
@@ -50,11 +50,11 @@ class WmShelf::AutoHideEventHandler : public ui::EventHandler {
   // Overridden from ui::EventHandler:
   void OnMouseEvent(ui::MouseEvent* event) override {
     shelf_layout_manager_->UpdateAutoHideForMouseEvent(
-        event, WmWindow::Get(static_cast<aura::Window*>(event->target())));
+        event, static_cast<aura::Window*>(event->target()));
   }
   void OnGestureEvent(ui::GestureEvent* event) override {
     shelf_layout_manager_->UpdateAutoHideForGestureEvent(
-        event, WmWindow::Get(static_cast<aura::Window*>(event->target())));
+        event, static_cast<aura::Window*>(event->target()));
   }
 
  private: